The present invention relates to a method for generating the light of LED lamp, in particular to a method for generating low color temperature light.
The present invention further relates to a light emitting device, in particular to a light emitting device for low color temperature light.
The simplest known LED may comprise a P-type semiconductor, a N-type semiconductor and a P-N junction between them. When the current travels through the LED, charge carriers (i.e. electron and hole) are generated in the P-N junction. Energy will be released in the form of photons as the electron and the cavity join together. Specified chemical materials may be added in the P-N junction so as to allow the light of specified color could be emitted by the LED lamp. For example, if InGaN is employed, the first wavelength light could be generated, and if GaN is employed, green light could be generated. The LED lamp is formed by encapsulating the LED with anode and cathode for connecting the power extending from the package colloid. Compared with the white light lamp such as minitype tungsten lamp and fluorescent lamp, the LED lamp is of the advantages including longer life time, energy saving, better reliability and durability, rapid reaction, less waste heat, adaptation to mass production, etc.
However, emission light with single wavelength of LED lamp can only be used in the specific decoration situation, and therefore a LED lamp with mixed colors used in various situations is the common object of the companies in this field. The method for generating such a LED lamp is to mix several kinds of single wavelength light so as to emit the desired color in different situations, such as white light, near-white light, amber light, etc, which is similar to color mixing on color palette to generate a specific color. In particular, the known methods for manufacturing the light mixing LED are mainly as follow:
1. LEDs of red, green and blue colors are encapsulated in one bulb, and an external circuit is provided for regulating the power of the tricolor LEDs. Thus, white light or near-white light could be obtained. In this structure, the powers of the three LEDs should be controlled separately, which results in the high complexity and costs for designing the peripheral circuit.
2. A LED emitting the first wavelength light (i.e. a blue LED) and a LED emitting the second wavelength light (i.e. a red LED) are used, and then the two LEDs are covered with yellow phosphor. After the light with the first wavelength irradiates on the yellow phosphor, one portion of the light travels through the yellow phosphor, while the rest of the light remains within the yellow phosphor to excite yellow light. The fist wavelength light (i.e. the blue light) and the second wavelength light (i.e. the red light) along with the yellow light are mixed together to generate white light or near-white light. In this structure, the desired voltage of the LED emitting the first wavelength light and that of the LED emitting the second wavelength light are very different, so that if the two LEDs are connected in series, high voltage is required, which is inconvenient for using, and if the two LEDs are connected in parallel, one of the two LEDs is required to be connected to a resistor, which increases the complexity of the manufacturing process and the costs of the LED lamp.
3. An ultraviolet LED is used. The ultraviolet radiation irradiates on the red, green and blue covering on the LED so as to generate red, green and blue light. The white light or near-white light is obtained by mixing by the red, green and blue light. However, a great amount of energy is released, when the ultraviolet radiation irradiates on the, which accelerates the aging of the phosphor and decreases the lifetime of the LED, and more seriously, hazardous substance is released after the ultraviolet radiation irradiates on the phosphor.
Moreover, the above methods are of the same problem that the emission light has a relatively high color temperature, and tends to be cold light which lacks of warm feeling as provided by the low color temperature light emitted from a minitype tungsten lamp or a high-pressure sodium lamp.